A novel wide-bandgap conjugated copolymer based on an imide-functionalized benzotriazole building block containing a siloxane-terminated side-chain is developed. This copolymer is successfully used to fabricate highly efficient all-polymer solar cells (all-PSCs) processed at room temperature with the green-solvent 2-methyl-tetrahydrofuran. When paired with a naphthalene diimide-based polymer electron-acceptor, the all-PSC exhibits a maximum power conversion efficiency (PCE) of 10.1%, which is the highest value so far reported for an all-PSC. Of particular interest is that the PCE remains 9.4% after thermal annealing at 80 °C for 24 h. The resulting high efficiency is attributed to a combination of high and balanced bulky charge carrier mobility, favorable face-on orientation, and high crystallinity. These observations indicate that the resulting copolymer can be a promising candidate toward high-performance all-PSCs for practical applications.

The cost‐effectiveness of polymer solar cells is a very important concern for future applications. In this work, a new combinatory side chain integrating siloxane terminal and alkoxy group is developed, and three polymers, PQSi05, PQSi10, and PQSi25, with 5%, 10%, and 25% contents of the siloxane‐terminated alkoxy side chain, respectively, are successfully synthesized. As the content of the combinatory side chain increases, the surface energy of the corresponding polymer film decreases, showing tunable miscibility in blend films with nonfullerene acceptor IT‐4F. A maximum power conversion efficiency (PCE) of 13.56% is achieved in the PQSi05:IT‐4F‐based device. The minor (5%) combinatory side chain approach retains a low synthetic complexity (SC) of 16.58% for PQSi05. Due to the improved device performance, a low figure‐of‐merit (FOM) of 1.22 is obtained for the PQSi05:IT‐4F blend. Furthermore, the contribution of the IT‐4F acceptor is considered for a comprehensive analysis, yielding an average SC (ASC) of 39.31% and an average FOM (AFOM) of 2.90. After statistical analyses and calculations, the PQSi05:IT‐4F is the best cost‐effective active layer to date. It is revealed that the introduction of the minor combinatory side chain is a promising strategy to develop high‐performing and cost‐effective polymer donors.

To thoroughly disclose the role of the siloxaneterminated side chain with different substituent positions, three difluorobenzotriazole−dithienylbenzodithiophene (FTAZ−BDTT)-based polymers PBZ-1Si, PBZ-2Si, and PBZ-3Si with the siloxane-terminated side chain on the FTAZ unit (PBZ-1Si), on the BDTT unit (PBZ-2Si), and both on BDTT and FTAZ units (PBZ-3Si), respectively, were synthesized. The different side chain substitutions have slight influences on absorption behavior, thermal stability, and frontier molecular orbitals but have shown a great effect on the aggregation of the polymers. Grazing-incidence wide-angle X-ray scattering measurements reveal that, relative to PBZ-1Si with branched alkyl on the BDTT unit, polymers PBZ-2Si and PBZ-3Si, bearing the siloxane-terminated side chains on the BDTT unit, exhibit smaller π−π stacking distances and larger crystal coherence lengths, suggesting that adopting the siloxane-terminated side chain on the BDTT unit can promote the interchain π−π interaction and the ordering of molecular packing. With IT-M as the non-fullerene acceptor, among the three polymers, the PBZ-2Si-based active layer possesses the highest ordered crystals for both polymers and IT-M as well as the purest domain, which affords efficient exciton dissociation, the most balanced hole−electron transport, and reduced recombination, leading to the highest short-circuit current density (J sc ) and fill factor (FF) and then the highest power conversion efficiency (PCE) of 11.14%. In contrast, PBZ-1Si-and PBZ-3Si-based devices show lower PCEs of 8.98 and 9.92%, respectively. Moreover, PBZ-2Si:IT-M also exhibits good thickness tolerance, and its thick active layer of 240 nm shows the most limited decrease of efficiency after 77 days of storage, supplying good potential for mass fabrication. Our work suggests that the fine pairing of a siloxane-terminated side chain and an alkyl side chain is beneficial for the optimizing of a conjugated polymer donor toward high-performance non-fullerene polymer solar cells.

Thickness-sensitive fill factors (FF) are usually encountered by organic active layers of several hundred nanometers, which significantly deteriorate photovoltaic performances of thick-film polymer solar cells (PSCs). Here, high hole mobility...

Herein, a high‐mobility polymer (Si25) pairing a nonfullerene acceptor (O‐IDTBR) is introduced to construct active layers of organic solar cells (OSCs). The OSCs based on Si25 and O‐IDTBR with comparable bandgaps of 1.61 eV show high open‐circuit voltage (Voc) of 1.03 V. Suitable energy level offsets between the donor and acceptor as well as sufficient photon absorbance by a 400 nm thick active layer afford a notable short‐circuit current (Jsc) of 21.11 mA cm−2, indicating a significantly suppressed trade‐off between Jsc and Voc among OSCs. In addition, notable high power conversion efficiency (PCE) between 10.2% and 11.54% can be achieved with thick blend films from 210 to 560 nm, a thickness range beneficial to pin‐hole free printing. The maximum PCE of 11.54% corresponds to a 400 nm thick blend film, which is a rare thickness for high‐efficiency nonfullerene‐based OSCs. The corresponding fill factors (FFs) are between 51.59% and 53.33%. The inferior FF is due to a very low electron–hole mobility ratio, offering space for future FF elevation. The results highlight the high Voc and Jsc potentials for thick‐film nonfullerene OSCs based on a high hole mobility donor as well as looking forward to a high electron mobility nonfullerene acceptor.

A new wide-band-gap conjugated polymer PBODT was successfully synthesized that showed high crystallinity and was utilized as the active material in nonfullerene bulk-heterojunction polymer solar cells (PSCs). The photovoltaic devices based on the as-cast blend films of PBODT with ITIC and IDIC acceptors showed notable power conversion efficiencies (PCEs) of 7.06% and 9.09%, with high open-circuit voltages of 1.00 and 0.93 V that correspond to low energy losses of 0.59 and 0.69 eV, respectively. In the case of PBODT:ITIC, lower exciton quenching efficiency and monomolecular recombination are found for devices with small driving force. On the other hand, the relatively higher driving force and suppressed monomolecular recombination for PBODT:IDIC devices are identified to be the reason for their higher short-circuit current density (J) and higher PCEs. In addition, when processed with the nonchlorinated solvent 1,2,4-trimethylbenzene, a good PCE of 8.19% was still achieved for the IDIC-based device. Our work shows that such wide-band-gap polymers have great potential for the environmentally friendly fabrication of highly efficient PSCs.

The design and synthesis of three n-type conjugated polymers based on a naphthalene diimide-thiophene skeleton are presented. The control polymer, PNDI-2HD, has two identical 2-hexyldecyl side chains, and the other polymers have different alkyl side chains; PNDI-EHDT has a 2-ethylhexyl and a 2-decyltetradecyl side chain, and PNDI-BOOD has a 2-butyloctyl and a 2-octyldodecyl side chain. These copolymers with different alkyl side chains exhibit higher melting and crystallization temperatures, and stronger aggregation in solution, than the control copolymer PNDI-2HD that has the same side chain. Polymer solar cells based on the electron-donating copolymer PTB7-Th and these novel copolymers exhibit nearly the same open-circuit voltage of 0.77 V. Devices based on the copolymer PNDI-BOOD with different side chains have a power-conversion efficiency of up to 6.89%, which is much higher than the 4.30% obtained with the symmetric PNDI-2HD. This improvement can be attributed to the improved charge-carrier mobility and the formation of favorable film morphology. These observations suggest that the molecular design strategy of incorporating different side chains can provide a new and promising approach to developing n-type conjugated polymers.

Molecular orientation in polymer solar cells (PSCs) is a critical subject of investigation that promotes the quality of bulk heterojunction morphology and power conversion efficiency (PCE). Herein, the intrinsic polymer orientation transition can be found upon delicate control over the branching point position of the irregular alkoxy side chain in difluoroquinoxaline−thiophene-based conjugated polymers. Three polymers with branching points at the third, fourth, and fifth positions away from the backbone were synthesized and abbreviated as PHT3, PHT4, and PHT5, respectively. Temperature-dependent absorption behavior manifests the polymer aggregation ability in the order of PHT3 < PHT4 < PHT5. Surprisingly, the polymer orientation transition from typical face-on to edgeon emerged between PHT4 and PHT5, as evidenced by X-ray-scattering analysis. The enhanced face-on crystallinity of PHT4 endowed the o-xyleneprocessed PHT4:IT-4Cl-based devices with the highest PCE of 13.40%. For PHT5 with stronger aggregation, the related o-xylene-processed PSCs still showed a good PCE of 12.66%. Our results demonstrate that a delicate polymer orientation transition could be realized through a precisely controlled strategy of the side chain, yielding green-solvent-processed high-performance PSCs.